Attention has been focused on a technique of forming a transistor (also referred to as a thin film transistor (TFT) or a field-effect transistor (FET)) using a semiconductor film formed over a substrate. The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image device (display device). As semiconductor films applicable to the transistors, silicon-based semiconductor materials are widely known, but oxide semiconductors have been attracting attention as alternative materials.
For example, a technique of fabricating a transistor using an In—Ga—Zn-based oxide as an oxide semiconductor is disclosed (see Patent Document 1, for example).
Conventionally, aluminum has been widely used as a material used for a wiring, a signal line, and the like, but, development using copper (Cu) is extensively conducted to further reduce the resistance. However, copper (Cu) is disadvantageous in that adhesion thereof to a film used as a base is poor and that the characteristics of a transistor easily deteriorate due to diffusion of Cu into a semiconductor film of the transistor.
Furthermore, a Cu—Mn alloy is disclosed as a material for an ohmic electrode formed over an oxide semiconductor film containing indium (see Patent Document 2, for example).